The present disclosure relates to digital microfluidic devices and methods.
Paper microfluidics, employing microfluidic channels formed within paper substrates, has recently emerged as simple and low-cost paradigm for fluid manipulation and diagnostic testing [1-3]. When compared to traditional “lab-on-a-chip” technologies, paper microfluidics has several distinct advantages that make it especially suitable for point-of-care testing in low-resource settings. The most obvious benefits are the low cost of paper and the highly developed infrastructure of the printing industry, making production of paper-based devices both economical and scalable [3]. Other important benefits include the ease of disposal, stability of dried reagents [4] and the reduced dependence on expensive external instrumentation[5,6].
While the paper microfluidics concept has transformative potential, this class of devices is not without drawbacks. Many assays have limited sensitivity in the paper format because of reduced sample volumes and limitations of colorimetric readouts [6]. These devices, being inherently channel-based, also exhibit large dead volumes as the entire channel must be filled to drive capillary flow. Perhaps the most significant challenge for paper-based microfluidic devices is a product of their passive nature itself, making it difficult to perform complex multiplexing and multi-step assays (e.g., sandwich ELISA).
There has been progress in expanding device complexity through the development of three-dimensional channel networks [7,8] and adapting channel length, width and matrix properties can provide control of reagent sequencing and time of arrival at specific points on the device [9]. Active “valve” analogues have also been demonstrated using cut-out fluidic switches [10] and manual folding [11] however, these techniques require operator intervention which can introduce additional complications.
Some groups have implemented complicated, multi-step assays including sandwich ELISA using paper “well plates” and manual pipetting [6,12-16]. These assays are analogous to those performed in standard 96-well polystyrene plates, but the “plates” are pieces of paper patterned with hydrophobic/hydrophilic zones. The drawback to this class of devices is that they are not truly “microfluidics”—unlike the methods described above, each reagent must be pipetted into a given well to implement an assay, similar to conventional multiwell plate techniques.